Synthesis of Tetrasubstituted 1,4-Dicarbonyl ( Z )-2,3-Dihaloalkenes via Electrophilic Halogenation of Alkynyl Hydrazones.

A highly practical and stereoselective route to 1,4-dicarbonyl 2,3-dihaloalkenes is presented. The strategy involves bench-stable unprotected alkynyl hydrazones and commercially available N -halosuccinimides that provide γ-oxo-α,β-( Z )-dihaloenoates in excellent yields with complete Z -selectivity. The protocol also furnishes vicinal dihaloalkenes with two different halogen atoms. Also, a straightforward one-pot synthesis of dihaloenoates from readily accessible 2-oxo-3-butynoate is demonstrated. In addition, potential synthetic transformations of 4-oxo-2,3-dibromoenoates are explored, which include the synthesis of valuable five- and six-membered heterocycles.